The present invention relates to spare keys for automobiles and/or for other purposes which may be retained on a card similar to a name card and can be put into a wallet or a pocket together with other things. Similar products may be seen in commercial markets, such as the disclosure as described in U.S. Pat. No. 4,637,236 in a spare key card. Some of these spare keys and retaining cards are matched with small protubelances and sunk spots while others are matched with tongues and grooves. Among them, the combining force between spare keys and cards formed by protubelances and sunk spots is weak and the keys are easily detachable from the cards. As for those spare keys and cards combined with tongues and grooves will take a lot of efforts to align the tongues and grooves which causes much inconvenience.